The purpose of this study is threefold: 1) To determine the tolerance and safety of pentoxyfilline in patients with ulcerative colitis and Crohn's disease. 2) To make preliminary observations on the efficacy of pentoxyifilline as a treatment for ulcerative colitis and Crohn's disease in order to design a more definitive double-blinded, placebo-controlled study. 3) To determine whether treatment with pentoxifylline reduces tumor necrosis factor alpha (TNF alpha) production by intestinal mononuclear cells isolated from the colonic mucosa of patients with inflammatory bowel disease, and to correlate this with the efficacy of pentoxifylline as a treatment for inflammatory bowel disease. This will serve as a first test of the hypothesis that TNF alpha plays a key role in inflammatory bowel disease.